普通化學 兩性物質?

HSO₄⁻ is NOT amphoteric.

The term "amphoteric" means that the species can be neutralized by both strong acids (H⁺) and strong alkalis (OH⁻).

All of HSO₄⁻, H₂PO₄⁻ and HPO₄²⁻ are anions of acid salts, and all anions of acid salts can be neutralized by strong alkalis.
HSO₄⁻ + OH⁻ → SO₄²⁻ + H₂O
H₂PO₄⁻ + OH⁻ → HPO₄²⁻ + H₂O
HPO₄²⁻ + OH⁻ → PO₄³⁻ + H₂O

HSO₄⁻ cannot be neutralized by strong acids. Otherwise, the H₂SO₄ formed is a strong acid which would completely dissociates to give back HSO₄⁻. In other words, there is no reaction.
HSO₄⁻ + H⁺ → no reaction
Since HSO₄⁻ can only be neutralize by strong alkalis but cannot by strong acids, HSO₄⁻ is NOT amphoteric.

However, H₃PO₄ and H₂PO₄⁻ are weakly acidic and only partly dissociate, and thus they can be neutralized by strong acids.
H₂PO₄⁻ + H⁺ → H₃PO₄ + H₂O
HPO₄²⁻ + H⁺ → H₂PO₄⁻ + H₂O
Since H₃PO₄ and H₂PO₄⁻ can be neutralized by both strong acids and strong alkalis, they are amphoteric.

Besides, H₂O is known to be amphoteric.